1. Field of the Invention
The present invention is directed to electromagnetic actuators. It finds particular, although not exclusive, application in valves employed to control liquid flow.
2. Background Information
The most common form of electrically operated valve employs a solenoid to drive a valve member into a valve seat and thereby stop flow through a conduit in which the valve seat is disposed. Although the tip of the valve member is in many cases made of a synthetic resin or other resilient material, most of the valve member is made up of a material of relatively high-magnetic-permeability material, such as steel, so that it will be subject to force from the solenoid""s magnetic field and act as a solenoid armature.
There are many applications in which electric-valve-control circuitry should employ as little power as possible. To this end, it is best for the valve member, which acts as the solenoid""s armature, to be as magnetically permeable as possible. But designers in the past have had to compromise permeability for corrosion resistance. Carbon steel, whose high magnetic permeability would otherwise make it desirable, is quite vulnerable to rust and corrosion. So designers have resorted to the higher-magnetic-permeability grades of stainless steel, even though stainless steel is less magnetically permeable than carbon steel.
Unfortunately, the ferromagnetic types of stainless steel tend not to be as corrosion-resistant as types of stainless that are not ferromagnetic, so the armature often needs to be subjected to a number of treatment steps to afford an acceptable level of corrosion resistance. These steps contribute to valve cost. Also contributing to cost is the greater solenoid-wire size required because the armature""s permeability is not as great as that of carbon steel.
We have developed a simple approach to reducing the need to make such armature-material comprises. Specifically, we so secure a flexible membrane over the end of the pocket in which the armature travels as to protect the armature""s high-permeability material from exposure to the possibly corrosive fluid whose flow the valve is to control. This would at first seem to impose a significant power cost, since it might be thought to subject the armature to the force imposed by the controlled fluid fluid""s pressure. But we eliminate this problem by adapting to it an approach previously used in arrangements such as that of U.S. Pat. No. 5,941,505 to Nagel to prevent leaks in membranes that protect the controlled fluids from valve-assembly contaminants.
As in those arrangements, we fill the armature pocket with an incompressible fluid so as to counterbalance the force exerted by the controlled liquid""s pressure. In contrast to those arrangements, though, we place the membrane in a position in which it protects at least the armature""s ferromagnetic portion from the fluid being controlled, as was just mentioned.